1. Field of the Invention
The present invention relates to an optical transmission system, and more particularly, to an optical receiver operating at high speed.
2. Description of the Related Art
As shown in FIG. 1, a conventional optical transmission system includes a light transmission terminal 10, which converts an electric signal into an optical signal and transmits the optical signal via a light transmission medium 20, and a light receiving terminal 30, which converts the optical signal back into an electric signal. In general, the light transmission terminal 10 includes a laser diode unit 120, which converts an electric signal into an optical signal and outputs the optical signal, and a transmission driver 110, which controls the light output power of the laser diode unit 120. The light transmission medium 20 may be made of plastic optical fiber (POF) or glass optical fiber (GOF). The light receiving terminal 30 includes a photodiode unit 310, a conversion amplifier 320 and a level converter 330.
The photodiode unit 310 converts a received optical signal into a current signal. The conversion amplifier 320 removes DC components from the current signal and amplifies the voltage. In the conversion amplifier 320, an analog signal is processed. The level conversion unit 330 converts the level of the analog signal output from the conversion amplifier 320 into a digital signal, suitable for operating CMOS circuitry.
The conversion amplifier 320 is very sensitive to noise. A circuit (not shown) within the conversion amplifier 320, which processes a signal having a relatively low level before the signal is amplified, is also sensitive to noise. Thus, it can be difficult to implement the conversion amplifier 320 together with the level converter 330, which generates switching noise, in a single chip. Therefore, in the conventional light transmission system, the conversion amplifier 320 and the level converter 330 are realized in separate chips, and thus, the integration density of a device is lowered and use of the device may be inconvenient.
Also, in the conventional light transmission system, the conversion amplifier 320 of the light receiving terminal 30 is formed to have a particular structure into which two signals can be input. In other words, the conventional conversion amplifier 30 has a differential input-differential output structure which enables it to receive a differential input signal and generate a differential output signal. Thus, to realize the characteristics of a photodiode, a dummy capacitor (not shown) is further included at a differential input terminal of the conversion amplifier 320, thereby realizing an actual capacitance of the photodiode. However, the capacitance of the photodiode may vary depending on a process for manufacturing the photodiode and the amount of reverse bias voltage applied to the photodiode, and thus, an actual dummy capacitance becomes different from the capacitance of the photodiode. As a result, since the amount and phase of noise input into the conversion amplifier 320 changes in the case of installing the dummy capacitor instead of the photodiode, the probability that errors occur increases. In addition, the capacitance of the photodiode in the light transmission terminal 30 is high, and thus, the operational speed of a system is lowered.
Therefore, a need exists for an optical transmission system implementing a conversion amplifier and level converter in one chip.
To solve the above problems, it is a first object of the present invention to provide an optical receiver implemented in one chip, thereby enhancing the integration density and the convenience of use.
It is a second object of the present invention to provide an optical receiver that reduces the influence of noise and the probability of error occurrence and can be operated at high speed.
Accordingly, to achieve the first object, there is provided an optical receiver that receives an optical signal, converts the optical signal into a current signal and extracts data. The optical receiver includes a current/voltage converter that converts the current signal into a voltage signal and outputs the converted voltage signal as a conversion voltage signal; a DC remover that removes DC components from the converted voltage signal; an amplifier that amplifies the output signal of the DC remover and outputs the amplified signal; and a level converter that converts the level of the output signal of the amplifier into a CMOS level and then outputs the converted signal as the data. The current/voltage converter, the DC remover, the amplifier and the level converter are implemented in one chip.
Preferably, a predetermined power voltage is supplied to the current/voltage converter, the DC remover, the amplifier and the level converter through power lines isolated from each other, thereby minimizing the influence of noise caused by the power lines.
To achieve the second object of the present invention, there is provided an optical receiver that receives a current signal from an optical receiving diode, which converts an optical signal into the current signal, and extracts data. The optical receiver includes a current/voltage converter that converts the current signal into a differential voltage signal and outputs the converted voltage signal as a conversion voltage signal; a DC remover that removes DC components from the conversion voltage signal; an amplifier that amplifies the output signal of the DC remover and outputs the output signal of the DC remover; and a level converter that converts the level of the output signal of the amplifier into a CMOS level. The current/voltage converter has a single input structure in which the current signal is input to one input terminal.
Preferably, the current/voltage converter includes a first bipolar transistor having a common base structure in which the current signal is input into the emitter of the first bipolar transistor and output to the collector of the first bipolar transistor.
The optical receiver of the present invention is implemented in one chip, thereby enhancing the integration density of the optical receiver and the convenience of use. In addition, the optical receiver of the present invention is less sensitive to noise, and thus the probability of error occurrence can be reduced and the optical receiver can be operated at high speed.